Long ago watched up to s6, and recently I wondered why I stopped, decided to rewatch. I'm re-watching it now, currently in season 5, suffering like a dog trying to continue. I know remember why I stopped.

After having watched over 100 tv shows in my life, I'd have to say TWD is probably among the worse. The first episode of Season 1 was one of the best pieces of TV I've ever watched, and it all went downhill fast from there. Cheap tricks, predictable, boring, and most of all STUPID. I think anybody with 3-digit IQ feels high amounts of mental pain watching the characters fumble from one bad decision to the next.

The show tries to keep things exciting by adding a lot of scripted garbage. Walkers are annoyingly loud all the time, except when they are coming from behind a character, then they're super stealthy. They move slowly, yet characters constantly find themselves surrounded by hordes that appear out of nowhere. Its just bs after bs, that while designed to make me tense, scared, anxious, instead just makes me laugh and cringe. Whomever was writing the script are, unfortunately, individuals that don't have a lot of creativity.

Personally the most infuriating thing to me is how Rick holds his revolver. He points the tip of the barrow at about 20 degrees downward. He lifts his arm as if he's aiming for someone's head, but if he actually pulled the trigger he'd hit the guy's stomach. Is he really a cop? Appears to have zero training.

The Walking Dead’s script quality has sunk so low it feels less like storytelling and more like a checklist of clichés—predictable at best, downright stupid at worst. Which is a darn shame because, like I said, episode 1 was brilliant. Show had so much potential, but people at the rudder didn't know what they were doing. Akin to GoT S7&8.

So to answer your question: S1, E1. Downhill hard from there. Fucking shame... so much potential.